1. Field of Invention
The present invention relates to an input/output (I/O) signal processing circuit and an I/O signal processing method; particularly, it relates to such an I/O signal processing circuit having a level adjustable I/O circuit and a corresponding I/O processing method.
2. Description of Related Art
Please refer to FIG. 1, which shows a block diagram of a conventional power supply system. The conventional power supply system 100 comprises a power supplier 10 which is for example a power adaptor, a cable 70 and a power receiver 20 which is for example an electronic device. The power adaptor 10 and the electronic device 20 are coupled to each other through the cable 70. The power adaptor 10 includes a power converter 11, a control circuit 12 and an input/output (I/O) circuit 62A. The control circuit 12 controls an operation of the power converter 11, and receives as well as transmits signals via the I/O circuit 62A. The electronic device 20 includes a load 21, a control circuit 22 and an I/O circuit 62B. The control circuit 22 controls an operation of the load 21 and receives as well as transmits signals via the I/O circuit 62B. The cable 70 includes a positive power transmission line 71, a negative power transmission line 73 and a signal transmission line 72. When the power adaptor 10 (as a power supplier) and the electronic device 20 (as a power receiver) are coupled to each other through the cable 70, the positive power transmission line 71 and the negative power transmission line 73 form a loop to transmit power. The signal transmission line 72 can transmit data (i.e., a communication signal CC) between a terminal CC1 of the power adaptor 10 and a terminal CC2 of the electronic device 20.
As shown in FIG. 1, because the positive power transmission line 71 has a parasitic resistance (represented by a resistor R1), when the power adaptor 10 supplies a current I through the positive power transmission line 71, there will be a voltage drop across the resistor R1. That is, there will be a voltage difference between the voltage VA and the voltage VB. Similarly, because the negative power transmission line 73 also has a parasitic resistance (represented by a resistor R2), there will be a voltage drop across the resistor R2 as the current I flows through the negative power transmission line 73. That is, there will be a voltage difference between the grounding terminal GNDA and the grounding terminal GNDB. As a consequence, the level of the communication signal CC will be inaccurate due to the unwanted level difference between the voltage VA and the voltage VB and the unwanted level difference between the grounding terminal GNDA and the grounding terminal GNDB. For example, a digital signal “1” might be misinterpreted as “0” because the communication signal CC has a voltage level which is too low relatively to the grounding level; or, a digital signal “0” might be misinterpreted as “1” because the communication signal CC has a voltage level which is too high relatively to the grounding level.
In view of the above, to overcome the drawbacks in the prior art, the present invention proposes an I/O signal processing circuit and an I/O signal processing method, which are capable of providing an accurate communication signal CC via a level adjustable I/O circuit.